Cooling apparatus for treating cutting tools



July 13, 1948.

A. L. NELSON COOLING APPARATUS on TREATiNG GUTTING 'rooLs Fil'ed March 3, 1945 INVENTOR, wfZbw 4 Patented July 13, 1948 COOLING APPARATUS FOR TREATING CUTTING TOOLS Arthur L. Nelson, Cincinnati, Ohio, assignor to Super Treat, Inc... Cincinnati, Ohio, a corpora! tlon of Ohio Application March 3, 1945, Serial No. 580,849

(or Tia-91.5)

- sOlaims. 1 This invention relates to a method and apparatus for the treatment of metals at sub-zero temperatures. The invention is disclosed particularly inrelation to the hardening of metal cutting tools, such as those of high speed steel, in which a more complete transformation of the metal to. a hardened state occurs when it is subiected to a very low temperature. 'The invention, however, is adapted to be used for other purposes where low temperatures are desirable.

j The cold treatment of metal cutting tools and bits has been Iound to prolong-tool life, and since the treatment is a relatively inexpensive one the process is finding-rather wide-spread usage in the machining industries. In the conventional technique the steel to be hardened is first heated to a high temperature, then is quenched in the usual manner, next is drawn and allowed to cool to room temperature, and then is exposed to a very low temperature, for instance, 80" C. In this last step the steel is physically transformed to its fully hardened and its stress-relieved condition.

Inasmuch as the degree of coldness to which the metal is subjected plays a part in the'physical conversion of the structure of the steel, the

principal purpose of this invention has been to provide a source of very low temperature without resorting to the extensive refrigeration equipment usually employed. The conventional rethe cost of the equipment, makes its use uneconomic'al unless the plant is run continuously.

'Thepresent invention contemplates an appaf ratus Iorchilling cutting tools and for similar operations, which can be used intermittently or as-and when required to produce a very low temperaturequickly, and to produce a temperj ature as low or lower than the temperatures available with the more complicated mechanical refrigeration apparatus. 1

It is also the object of this invention to provide a method of producing low temperatures and particularly oichilling cutting tools which provides a desirable hardening eflect without the utilization of costly equipment.

In addition to the low temperature chilling "installations which have been available in the past, there have been available small refrigerators in which the low temperature has been 2 provided by immersing solid carbon dioxide, Dry Ice, in an organic solvent, such as methanol. Dry Ice and methanol stabilize at a temperature of 80 C. and, while treating tools at this temperature is in some cases beneficial, still greater advantages are obtained if a temperature 10 to 15 lower is utilized. In the past it has been the practice to immerse the tools in.the alcohol in when the Dry Ice is disposed and to preserve the life of the Dry Ice by maintaining the vessel containing it under positive vapor pressure.

I have discovered and determined that if a subatmospheric or negative pressure is utilized in place of the positive pressure, then the temperature of the solution is substantially lowered. The decrease in temperature, which thus may be obtained, is sufiicient to provide a pronounced beneficial effect on the tools being treated. While it has been known that reduced pressure tends to volatilize a liquid and that the volatilization reduces temperature, still it has not been appreciated that, working at the extremely low temperatures specified,a reduction 01 pressure accomplishes a lowering of temperature of significant importance in respect to the tools being treated, but without dissipating the cold producing substances at a prohibitive or undesirable rate.

For instance, fifty pounds of cutting tools ma be immersed in forty-two pounds of methanol in which seventy-four pounds of Dry Ice is immersed, the treating vessel subjected to approximately twenty-two inches of vacuum and the treatment continued for about 10.2 hours with the loss of only four pounds of methanol and twenty-nine pounds of Dry Ice. This degree of vacuum lowers the temperature of the treating solution to -92 C. and maintains it at that point for the entire duration of the treatment. The average life of the tools so treated is substantially greater than the average life of tools treated in the same solution, say at 80 C..

such as is obtained under atmospheric pressure or positive pressure.

In the accompanying drawings, Figure 1 represents one type of equipment adapted for carrying out the processes described and Figure 2 represents the modifications of the apparatus described inF'igure 1. Each figure discloses a vertical sectional view of the equipment.

In Figure l, the numeral l indicates a cylindrical box or cabinet consisting of an outer shell 2 and an inner shell 3 spaced apart from one another and connected by a top member 4. Suitable low temperature insulation 5 is disposed seal for the cabinet.

Within the inner shell rail members l2 are disposed andthese are adapted to suspend the basket I3 by its rail members H, in which the tools or other articles being treated are to be disposed. The bottom and sides of the basket contain perforations IE to permit circulation of the coolant 18 which is disposed in the inner shell. The basket is provided with a perforated lid 11 having a handle l8, as disclosed, for lowering and raising the basket in relation to the coolant, but the lid is not strictly necessary. Near the bottom of the inner shell is a pipe I3 for drawing oi! the cooling solution. A valve 20 is disposed in this pipeline. Adjacent to the top of the inner shell and above the level of the cooling solution a pipe 2| is disposed. This pipe is connected to a source of sub-atmospheric pressure 22 having a vent 23. The source of sub-atmospheric pressure, for instance, a vacuum pump, is operated by a motor 24, as disclosed, though any mechanism for providing negative pressure may be employed.

The apparatus disclosed in Figure 2 is generally similar to that disclosed in Figure 1, the main difference being that the insulating material of the apparatus disclosed in Figure 1 is omitted, and the vacuum drawn on the apparatus is utilized not only to lower the temperature of the cooling solution, but also to insulate the compartment in which the tools are immersed. More specifically, the apparatus disclosed in Figure 2 comprises an outer shell 25 which is preferably cylindrical in configuration. Projecting inwardly from the outer shell at its top is a flange or top member 26. The lid or cover member has a handle 21, a gasket 28 and is similar to th lid or cover member disclosed in Figure 1 except that the insulation or packing is omitted and an aperture 29 is provided in the bottom of the lid so that its interior is exposed to the vacuum to which the cooling solution is subjected. An inner shell or compartment 30 for holding the cooling solution is provided. On the inside of this compartment rails 3| are provided for holding the basket 32 adapted to hold the tools being treated. The rails 33 on the basket cooperate with the rails 3! extending inwardly from the inner shell to provide the support for the basket. The latter is provided with perforations 34, a perforated lid 35 having a. handle 36, all as disclosed in Figure 1. The basket rests upon pedestals 31 and is also supported at its top by brackets 38 having lower flanges 39 adapted to engage a top flange 40 extending outwardly from the inner shell. These brackets at their tops have inwardly. turned flanges 4| which extend downwardly at their ends 42 to seat and center the lid. Adjacent'to the bottom of the inner shell is a pipe 43 for withdrawing the cooling solution, the flow of solution being controlled by valve 44. The entire interior of the cabinet of Figure 2 is connected wit a source of sub-atmospheric pressure 45 by means of a pipeline 45. The source of sub-atmospheric Pressure is provided with a vent 41 and is operated by a motor 48, though any type or equipment for achieving a sub-normal pressure may be employed.

The partial vacuum, of course, tends to draw oif both the methanol and the gaseous carbon dioxide; the two together constitute a mixture which is a non-explosive so that the method creates no fire hazard. One outstanding advantage of the process is that the: lower temperature is created at the surface of the methanol. The liquidat the surface, chilled by the evaporation, thus tends to descend in the vessel creating a current about the tools being treated. When the va'cuum is first drawn the temperature 01 the methanol is g-80 C.; as a result of the circulation the temperature of the entire body of treating liquid is reduced to 92 C. Thereafter any tendency of the temperature to drop results in circulation which maintains the low and even temperature of the entire body of liquid. This circulation, of course, removes a greater amount 01 heat from the tools in a shorter amount of time than would be thecase were the liquid stagnant.

Instead of methanol, other volatile liquids may be employed, provided they do not become solid at the low temperature achieved. Typical examples of liquids suitable for use in this process are methyl acetate, acetyl chloride, amyl chloride, amyl bromide, sec. butylamine, butyl bromide, butyl chloride, butyl iodide, sec. butyl iodide, butyl ethyl ether. butyl methyl ether, ethyl alcohol, isobutyl bromide, isothiocyanic acid, pentane, 2,2-dimethyl pentane, 3,3-dimethyl, Z-propanethiol, propenyl bromide, propyl alcohol, propyl bromide, propyl ether and methylene chloride.

It is believed that the sub-atmospheric pressure hastens the evaporation of Dry Ice and thus lowers its temperature and also that it evaporates the methanol or the other liquid used, thus lowering its temperature also. The total lowering of temperature is greater than would be anticipated at the low temperature involved. It is believed that the evaporation of the carbon dioxide isotropically assists in evaporating the methanol at this very low temperature, though this invention is not predicated on this theory. In any event, very low temperatures of the nature specified are obtained without such consumption of materials as would make the process prohibitive economically. The method and apparatus are adapted to be used on batches of tools whenever it is desirable to harden a given quantity. The apparatus need not be run continuously; on the contrary, to start the apparatus operating, it is only necessary to immerse Dry Ice in the methanol, then pull a vacuum on the equipment.

Having described my invention, I claim:

1. An apparatus adapted for use in the cold treatment of cutting tools, said apparatus comprising an outer shell and an inner shell spaced from it, the latter adapted to hold an organic liquid and solid carbon dioxide, the interiors of said shells being sealed from the atmosphere and communicating with each other in the upper portion of said apparatus, means for holding cutting tools immersed in liquid contained within the inner shell, and means for establishing a sub-atmospheric pressure within said interiors so that a partial vacuum in said interiors both lowers the temperature within the inner shell, and insulates the inner shell thermally from the outer shell;

2. An apparatus adapted for use in the cold treatment of cutting tools, said apparatus comprising an outer shell and an innershell spaced from it, the latter adapted to hold an organic 5 liquid and solid carbon dioxide, the interiors of said shells being sealed from the atmosphere and communicating with each other in the upper portion of said apparatus, an open work basket positioned within and in spaced relation to walls of the inner shell and adapted forholding cutting tools immersed in liquid contained within the inner shell, and means for-establishing a subatmospheric pressure within said interiors so that a partial vacuum in said interiors both lowers thetemperature within the inner shell and insulates the inner shell thermally from the outer shell.

3. An apparatus adapted for use in the cold treatment of cutting-tools, said apparatus comprising an outer shell and an inner shell spaced from it, the latter adapted to hold an organic liquid and solid carbon dioxide, the interiors of said shells communicating with each other in the upper portion of said apparatus, a hollow lid adapted to cover an opening in the upper portion of said shells, said lid having spaced inner and outer walls, means for holding cutting tools immersed. in liquid contained within the inner shell, means connecting the space between said shells with the space between the walls of said lid, and means REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS Number Name Date 1,936,214 Sommers Mar. 21, 1933 2,148,109 Dana Feb, 21, 1939 2,229,437 Birdsall Jan. 21, 1941 OTHER REFERENCES The Tool Engineer, Jan. 1944, DD. 99, 101, 102 and 104, especially p. 104.

' Transactions of American Society for Metals, vol. 30, pp, 569 through 592, especially pp. 577 and 586. g

the 

